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Е ТЕХНОЛОГИИ В КОСМИЧЕСКИХ ИССЛЕДОВАНИЯХ ЗЕМЛИ, Т 11 № 5-2019 ИИ НА АНГЛИЙСКОМ ЯЗЫКЕ: РАДИОТЕХНИКА И СВЯЗЬ
doi: 10.24411/2409-5419-2018-10289
DETERMINATION OF THE READINESS FACTOR OF FIBER OPTICAL COMMUNICATION LINES AT TEMPERATURE IMPACTS ON OPTICAL FIBERS
IGOR V. BOGACHKOV1 ABSTRACT
The operational experience of fiber optical communication lines has shown that the service SERGEY S. LUTCHENKO2 life time of an optical cable depends on both a mechanical strain in optical fibers and their
temperature. Segments of overhead cable line can be subjected to essential temperature changes. Cable elements, means of its fastening, line materials have different heat-expansion indexes. Essential mechanical strains take place in the case of significant changes in temperature due to the uneven expansion of the contacting materials within the fiber. To provide a failure-free service of fiber optical communication lines a steady monitoring of optical fibers is needed for timely detection of suspicious segments. Brillouin reflectometers are applied to detect the optical fiber segments with higher strain and temperature changes. The results obtained confirm that the temperature changes in optical fiber impact the readiness index of fiber optical communication lines. Typical Brillouin traces for optical fiber segments with changed temperature are depicted. The estimation technique of the communication line reliability taking into consideration the temperature impacts on fibers is proposed. Reliability of the communication line is estimated by the readiness index. The investigations were carried out using Markov chain theory. The permitted value of the readiness index is calculated after validation of the communication line states, construction of the graphs and system transitions, estimation the true and observed time in given states. The permitted value allows the frequency of maintenance of communication lines to be determined. Process modeling of signal propagation in the optical fiber enables the performance of the communication line reliability taking into account the above equations to be determined. The employment of the Brillouin reflectometer in the control systems increases its reliability and detects the suspicious segments in optical fibers in advance.
Information about authors:
1 PhD, Docent, Associate professor of Omsk State Technical University, Senior Member IEEE, Omsk, Russia, bogachkov@mail.ru;
2PhD, Docent, Associate professor of Omsk State
Technical University Omsk Russia KEYWORDS: optical fiber, strain; fiber optic communication line; temperature impact;
lutchenko_s@inbox.ru reliability; mathematical model; readiness factor.
For citation: Lutchenko S.S., Bogachkov I.V. Determination of the readiness factor of fiber optical communication lines at temperature impacts on optical fibers. H&ES Research. 2019. Vol. 11. No. 5. Pp. 66-72. doi: 10.24411/2409-5419-2018-10289
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The operational experience of fiber optical communication lines (FOCLs) has shown that the service life time of the optical cable depends on both a mechanical strain in optical fibers (OFs) and their temperature [1-3].
Segments of the overhead optical cable can be subjected to essential temperature changes. For example, the optical cable sheath can be heated to a high temperature (about +60 °C) in some segments in summer, and it can be cooled to -40 °C in winter [3-6]. In addition, the temperature of the adjacent segments of optical cable, one of which is under direct sunlight and the other is in the shade, will vary significantly.
This may result in nonreversible changes in the optical fiber in the FOCL because of the higher mechanical strains in the optical fiber, which can reduce the service life time of the optical cable in general [1, 2, 5].
Cable elements (optical fiber, protective members and jackets), means of its fastening, the medium of laying and line materials have different heat-expansion indexes. Essential mechanical strains take place in the case of significant changes in temperature due to the uneven expansion of the contacting materials within the OF [5-8].
To provide a failure-free service of FOCL a steady monitoring of optical fibers is needed for timely detection of suspicious segments [1, 5, 7].
Brillouin optical time domain reflectometers (BOTDRs) are applied to detect the OF segments with higher mechanical strain and temperature changes. The distribution of a Mandelstam — Brillouin backscattering spectrum (MBBS) along the OF is evaluated and assayed in BOTDR [1-3].
In this paper we analyze the Brillouin reflectograms for the segments of optical fibers with changed temperature.
Fig. 1 - Fig. 4 illustrate the Brillouin traces for segments with temperature changes obtained in investigation tests with OFs [1, 5, 7].
In investigation tests, the results of which are given below, the light pipe is composed of single mode optical fibers: G. 652 OF (usual optical fiber), welded with G. 657 fiber, which in turn is welded with G.653 optical fiber (DSF — dispersion-shifted fiber) [5].
Fig. 1 demonstrates the Brillouin reflectogram of the MBBS distribution along the light pipe with heated segments to +90 °C (indicated by solid thick arrows "H"). Solid arrows "1", "2", "3" correspond to unheated segments, depending on the OF type: G. 652 — "1" connected to G. 657 OF — "2", which in turn is welded with G. 653 (DSF) — "3".
Every cross-section of BOTDR-reflectogram along the distance axis is the reflectogram for a fixed frequency. Every cross-section along the frequency axis is the MBBS profile in this OF section [1, 5]. Both the MBBS peak for the specified line coordinate and the response of MBBS profile in this OF section are depicted in the lower right corner of the reflecto-gram. For example, the peak of MBBS (f — Brillouin frequency shift) is displayed at a frequency of 10.847 GHz in the cross-section of OF at the distance of 949.96 m with a width of MBBS of 193.4 MHz and a level of the received backscattered signal at a maximum of 84.30 dB.
The heated segments occur according to shift offB in the direction of a frequency upshift (F2).
Fig. 1. Trace of the MBBS along a light pipe with heated segments to +90 °
ч\ч -о ^/у//
НАУКОЕМКИЕ ТЕХНОЛОГИИ В КОСМИЧЕСКИХ ИССЛЕДОВАНИЯХ ЗЕМЛИ, Т БЛИКАЦИИ НА АНГЛИЙСКОМ ЯЗЫКЕ: РАДИОТЕХНИКА И СВЯЗЬ
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Fig. 2 shows the respective strain pattern in the light pipe (with some heated segments to +90 °C), which is achieved after the MBBS reflectogram processing (Fig. 1).
The tested segments of the light pipe are marked by markers: "1-2" — G. 652, "3-4" — G.657, "5-6" — G.653. Strain values in these segments are distinguished at the bottom
of the reflectogram. When evaluating the strain, we use the initial level fB0 as a typical value for G. 652 fiber [5, 7].
As a result, the strain in the heated segment for all tested OFs increased by an average of 0.16%.
Fig. 3 shows the strain pattern in the OF with cooled segments of the same light pipe to -10 °C.
Fig. 2. Strain pattern with heated segments to +90°
Fig. 3. Strain pattern along the light pipe with cooled segments to -10 °
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The frequency downshift fB is observed in cooled segments.
Evaluation of the strain patterns illustrates a decrease in the OF strain by an average of 0.07% in the cooled segments [5].
As a comparison, the strain pattern in the optical fiber at the room temperature (+25 °C) for the same segments of the light pipe is shown in fig. 4.
Heedless of the fact that the strains in the optical fibers of FOCL are no more than potentially disruptive value (0.2% [1, 5]), the temperature changes in the OFs of the FOCL can alarm the suspicious segments (burst main, cracks in protective structures, unauthorized access, etc.). These phenomena may become a cause of the degradation failure of members of optical cables and fibers, therefore it is necessary to detect them in advance [1-3, 5, 8].
In such a way the impact estimation of this phenomena on the FOCL reliability is of practical interest.
We analyzed the dependence of readiness index of the FOCL on the optical fiber temperature.
The route is seen to be ready for operation if both of its directions are in readiness. There are the following performances of readiness in G.821 recommendation: a readiness index of K.„ and an unreadiness index of K The readiness
AF U.
index is the ratio of time during which the route is in readiness to the overall period of monitoring. The unreadiness index is the ratio between the time during which the route is in unreadiness and the overall period of monitoring. Markov chain theory and probabilistic mathematical modeling are used to estimate the index [7, 9].
We made the following steps to get a mathematical model.
1. We find out the states in which the FOCL may be located.
2. A graph of states and transitions of the system is constructed.
3. We determine the system transitions from S. to SSj state.
4. Equations for the readiness index are written.
Fiber optical communication line has following states:
S0 — operational state;
S — condition under temperature impact on an optical cable;
52 — detectable failure state;
53 — nondetectable failure state;
54 — fictitious failure state;
STO — maintenance of an operational system;
S1TO — maintenance at temperature impact on the optical cable;
S3TO — maintenance in case of a nondetectable failure.
The graph of conceivable states of the FOCL is illustrated in Fig. 5.
At the time of t = 0 the operational system starts working, which is equivalent of the state of S0. The system operates continuously the time of T (periodicity time or cycle). It is necessary to perform system monitoring and maintenance every time equal to T [10-12].
During operation the system may be subjected to external impacts such as excessive heating or cooling. In this case the system will pass into a state of Sv At the state of SS1 the overtolerance loads will affect the system and it will fail. In this case, the system will pass into a detectable failure state of S2. A system failure is a transition to the S2 state. If during the time T the failure does not occur, the system goes into the state of S1T0. The system is in the state of S1T0 for the time tn required to monitor it. The transition of the system from the state of S1T0 to the state of S2 is possible which corresponds to the system failure.
946 OF1 l-j-2 OF 2 m -3 OF 3 963 m
ruII m 950 m 95( 2-
O.QJI373 ka J 1 O.OOiSS k-/ I I O.XtIf k> ||
Dlatuncaij a.«»o>4 km | Mnlui -O.TS94 K Lb(O) t ¡HO. OMWIIx I ■ . O if 4.7H | > l(b . VMHw JO . 4MOOH«
1 M«, kr7> - V 0.00143 lu> O.OU3 * (AVE) O.Ol» (MAX) O . 0196 % CH1H) O . 004 / K Hirknr .1 a Hsz-kor S-S 0.0070C km 0.00443 km o.oon; * o.oiiiz -»t (AVE) -0.04179 * (AVI) O ■ V 4 * (max) -o.oioe k (max) -o.cen (MI*J -O.V411 % (MlH) -O. HS75 M
Fig. 4. Pattern of the strain distribution in a light pipe at room temperature
НАУКОЕМКИЕ ТЕХНОЛОГИИ В КОСМИЧЕСКИХ ИССЛЕДОВАНИЯХ ЗЕМЛИ, Т 11 № 5-2019 ПУБЛИКАЦИИ НА АНГЛИЙСКОМ ЯЗЫКЕ: РАДИОТЕХНИКА И СВЯЗЬ
Fig. 5. Graph of states of a FOCL
The transition into the nondetectable failure state is due to the diagnostics error of second type. A possible reason for the system transition from the S1T0 to the S3 is an incorrect choice of performances in the test module (in reflectometer) of the OF monitoring system, leading to a formation of "dead zone" having the non-fixed irregularities. If there is no failure in the S1TO state, the system passes into the operational state of S0 after that the operating cycle is repeated.
If the system operates a time no more than T in the state of S0 and then fails, it means that system will pass into a detectable failure state of S2 If the system operates properly the time T in the state of S0, it will pass into the maintenance of an operational system of Sra. In this state the system is monitored
for a time t.
p
Here we consider a nondetectable failure state of S3. The system goes into this state only when it is monitored and the system is in it until the next check In this situation, it will obviously pass into the maintenance in case of a nondetectable failure of S3TO. During the test, the nondetectable failure will be detected and then the system will go to a detectable failure state of S2 and then it will return into the S0. If the failure is unfound, the system will return into the state of S3 The return cause of the system to the nondetectable failure state of S2 is error P2.
The system has a fictitious failure state of S4. Fictitious failure occurs due to the diagnostics error of first type of built-in diagnostic equipment. Timely detection of the fictitious failure returns the system to its initial state. Each time when the system returns to the state of S0 the operating cycle is repeated.
The technique of determination of the readiness index is considered in detail in [7, 12].
The readiness index is found by the following algorithm:
1. The matrix of transition probabilities (P) is written in accordance with the graph of system states (fig. 5).
2. A row matrix of final probabilities (n) is determined [7, 9, 12].
n = \no (T), n, (T), n2 (T), n3 (T), n4 (T)|. (1)
3. The final probabilities of the system in each state are determined. In order find it we need to multiply the matrix of transition probabilities by the row matrix of final probabilities and perform the necessary transformations [11, 12].
n = n- P
En-=1
. (2)
4. To determine the readiness index of the FOCL is necessary to estimate the real time of <».(7) and the current time of u.(T) for the system in certain states.
The real time is found for the following states: S0, SS1 and S4.
ra,
i
(T )=Ep у JVF/ Ь).
(3)
J 0
where p.. is the transition probability from this state, t .. is the time for a system in this state, F..(t.) is the distribution function for this step of process [1,7, 12]."
The current time is determined for the following states:
S0, S1, S2, S3 and S4.
(4)
To calculate the readiness index of KAF(T) we use the above functions for the final probabilities n(T) (1) — (2), for the real ra.(T) (3) and the current u.(T) (4) time.
An equation for the readiness index of KAF(T) is given by:
Kaf (T) =
П (T )ffl0 (T) + n (T)ffl, (T) + n, (T )ffl4 (T)
n0 (T )v„ (T) + n (T) v, (T) + n2 (T )v2 (T) + П3 (T )v3 (T) + n, (T )v, (T) (5)
The method for calculation of the reliability performances is difficult and time-taking process. To find the reliability performances we apply the mathematical programs ("MathCAD"), which have the possibility of both numerical and symbolic solution of many tasks, having a mathematical apparatus to calculate the linear algebraic equations [7, 11, 12].
Using the results achieved after calculation, a dependence graph of KAF(T) is constructed, which may be useful for us to determine an allowable time between checks.
Fig. 6 shows the dependency graphs of KAF(T) on temperature of OF obtained using modeling, which enable us to confirm temperature impacts of the OF on the readiness index of the FOCL.
The graphs are presented for three various temperatures of OF: the first value ("1") corresponds to +25 °C (room temperature), the second ("2")—+60 °C, the third ("3")—minus 40 °C.
Fig. 6. Dependency graph of KAF{T) on temperature of OF
The conducted tests show that temperature changes in OF impact the reliability performances of FOCL [7, 12].
Process modeling of optical signal propagation in an OF enables the performance of FOCL reliability taking into account the above equations to be determined.
The employment of the BOTDR in the FOCL sensitively increases its reliability and detects the suspicious segments in OFs in advance.
The work was carried out with the financial support ofthe Ministry of Education and Science of the Russian Federation within the scope of the base part of a State Assignment within the sphere of scientific activity (Project No. 8.9334.2017/8.9).
References
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2. Kobyakov A., Sauer M., Chowdhury D. Stimulated Brillouin scattering in optical fibers. Advances in Optics and Photonics. 2010. Vol. 2. Issue 1. Pp. 1-59.
3. Bao X., Chen L. Recent Progress in Brillouin Scattering Based Fiber Sensors. Sensors. 2011. Vol. 11. Pp. 4152-4187.
4. Lyubchenko A.A., Kopytov E. Y. Determination of preventive maintenance reasonable intervals for moving constraint systems. Instruments and Systems: Monitoring, Control, and Diagnostics. 2012. No. 1. Pp. 20-24.
5. Bogachkov I. V Temperature Dependences of Mandelstam— Brillouin Backscatter Spectrum in Optical Fibers of Various Types. Proceedings of the conference Systems of Signal Synchronization, Generating and Processing in Telecommunications (SINKHROINFO-2017), Kazan, Russia, 3-4 July 2017. New York: Curran Associates, Inc, 2017. Vol. 8. No. 1. Pp. 50-55.
6. Zou W., Long X., Chen J. Brillouin Scattering in Optical Fibers and Its Application to Distributed Sensors. In book: Advances in Optical Fiber Technology: Fundamental Optical Phenomena and Applications. Intech, 2015. Chapter 1. Pp. 1-53.
7. Bogachkov I. V., Lutchenko S. S. Reliability assessment of fiber optic communication lines depending on external factors and diagnostic errors. Journal of Physics: Conference Series. International Conference Information Technologies in Business and Industry, Tomsk, 17-20 January 2018. New York: Curran Associates, Inc, 2018. Vol. 1015. Pt.1. Pp. 26-32.
8. Ruiz-Lombera R., Fuentes A., Rodriguez-Cobo L., Lopez-Higuera J. M., Mirapeix J. Simultaneous temperature and strain discrimination in a conventional BOTDA via artificial neural networks. Journal of Lightwave Technology. 2018. Vol. 36. No. 11. Pp. 2114-2120.
9. Lyubchenko A., Castillo P.A., MoraA. M., García-Sánchez P., Arenas M. G. Simulation approach for optimal maintenance intervals estimation of electronic devices Automation Control Theory Perspectives in Intelligent Systems: Proceedings of the 5th Computer Science On-line Conference 2016 (CSOC2016). Series: Advances in Intelligent Systems and Computing. Springer, Cham, 2016. Vol. 466. Pp. 153-164.
10. Minardo A., Bernini R., Zeni L. Bend-Induced Brillouin frequency shift variation in a single-mode fiber. IEEE Photonics Technology Letters. 2013. Vol. 25. No. 23. Pp. 2362-2364.
11. Maistrenko V.A., Bogachkov I. V. Kopytov E. Y., Lyubchenko A. A., Lutchenko S. S. Castillo P. A. An approach for estimation of integrated reliability indices and maintenance intervals of fiber-optic communication lines. Proceedings of the conference Actual Problems of Electronic Instrument Engineering, Novosibirsk, 03-06 October 2016. Novosibirsk, 2016. Vol. 1. Pp. 64-68.
12. Lutchenko S. S., Kopytov E. Y., Bogachkov I. V. Assessment Of Fiber Optic Communication Lines Reliability With Account Of External Factors Influence. Proceedings of the conference IEEE Dynamics of Systems, Mechanisms and Machines (Dynamics), Omsk, Russia, 13-15 November 2018. Omsk, 2017. Pp. 1-5.
НАУКОЕМКИЕ ТЕХНОЛОГИИ В КОСМИЧЕСКИХ ИССЛЕДОВАНИЯХ ЗЕМЛИ, Т
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БЛИКАЦИИ НА АНГЛИЙСКОМ ЯЗЫКЕ: РАДИОТЕХНИКА И СВЯЗЬ
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ОПРЕДЕЛЕНИЕ КОЭФФИЦИЕНТА ГОТОВНОСТИ ВОЛОКОННО-ОПТИЧЕСКИХ ЛИНИЙ СВЯЗИ ПРИ ТЕМПЕРАТУРНЫХ ВОЗДЕЙСТВИЯХ НА ОПТИЧЕСКИЕ ВОЛОКНА
ЛУТЧЕНКО Сергей Святославович, KEYWORDS: оптическое волокно; натяжение; волоконно-оптиче-
Омск, Россия, lutchenko_s@inbox.ru ская линия связи; температурное воздействие; надёжность; мате-
матическая модель; коэффициент готовности.
БОГАЧКОВ Игорь Викторович,
Омск, Россия, bogachkov@mail.ru
АННОТАЦИЯ
Практика эксплуатации волоконно-оптических линий связи (ВОЛС) показала, что срок службы оптического кабеля зависит от механических натяжений его оптических волокон (ОВ), а также от их температуры. Участки кабелей, проложенных с использованием подвесной технологии, могут испытывать существенные перепады температуры. Например, летом оболочка кабеля может на некоторых участках нагреваться до высокой температуры, а зимой может сильно охлаждаться. Это может привести к необратимым изменениям в ОВ ВОЛС, связанным с появлением повышенных механических напряжений в ОВ, что может значительно сократить срок службы кабеля в целом. Элементы кабеля, средства его крепежа, среда прокладки и материалы линии имеют различные коэффициенты теплового расширения. В случае существенных изменений температуры из-за неравномерного расширения соприкасающихся материалов внутри ОВ также могут возникать существенные механические натяжения. ля обеспечения бесперебойной работы ВОЛС необходим постоянный мониторинг ОВ для своевременного выявления проблемных участков. Для обнаружения напряжённых участков ОВ или имеющих изменённую температуру, применяются бриллю-эновские оптические импульсные рефлектометры (БОИР). На основании проведённых оценок можно сделать вывод, что изменение температуры ОВ оказывает влияние на показатели готовности ВОЛС. Приведены характерные БОИР-графики участков ОВ с изменённой температурой. Рассмотрена методика оценки
надёжности ВОЛС с учётом влияния температуры на её ОВ. Надёжность ВОЛС оценивается по коэффициенту готовности. Исследования выполнены с применением теории цепей Маркова и вероятностного математического моделирования. Допустимое значение коэффициента готовности определяется после обоснования состояний ВОЛС, составления графов и переходов системы, вычисления истинного и наблюдаемого времени нахождения системы в заданных состояниях, и позволяет определить предельную периодичность обслуживания ВОЛС. Моделирование процессов распространения оптического сигнала в ОВ с учетом приведенных формул позволяет определить характеристики надежности ВОЛС. Включение БОИР в систему мониторинга ВОЛС существенно повышает её надёжность, так как позволяет заблаговременно обнаруживать проблемные участки в ОВ.
Работа выполнена при финансовой поддержке Министерства образования и науки РФ в рамках базовой части госзадания в сфере научной деятельности
(проект № 8.9334.2017/8.9).
СВЕДЕНИЯ ОБ АВТОРАХ:
Лутченко С.С., к.т.н., доцент; доцент Омского государственного технического университета;
Богачков И.В., к.т.н., доцент; доцент Омского государственного технического университета, Член IEEE.
Для цитирования: Лутченко С.С., Богачков И.В. Определение коэффициента готовности волоконно-оптических линий связи при температурных воздействиях на оптические волокна // Наукоемкие технологии в космических исследованиях Земли. 2019. Т. 11. № 5. С. 66-72. Сок 10.24411/2409-5419-2018-10289
